Acquisition of data through transmission of the data from a remote source is desirable when the data source is inaccessible for direct processing of the data. For example, when acquiring data from a well such as a gas or oil well, the data must be collected within the well and transmitted from the well to a surface source for processing. This can involve provision of a signal transmission line, a control line, and a power line into and from the remote data source. When such lines constitute electrical connections to the remote data source, such electrical lines can create further data acquisition problems due to the generation of electromagnetic noise in the signal lines, as well as crosstalk between the lines if the lines are not adequately shielded.
The power line may also be dispensed with if a power source such as a battery can be located at the remote power source. However, this may necessitate periodic replacement of the power source, which may not be simple if, for example, the battery is located within a well or in a radioactive area from which data is to be remotely sampled.
It is also possible to use optical fibers rather than electrical lines for both data transmission as well as for control lines to control the transmission of data. The use of optical fibers, rather than electrical lines permits higher quality data transmission free of noise generated by conventional electrical lines.
Blackburn U.S. Pat. No. 3,984,824 describes a system wherein an analog signal is fed into a transmitter which amplifies the signal and feeds it to an LED wherein the electrical signal is converted to a light signal which is transmitted over an optical fiber to a receiver where the light output is converted back to an electrical signal via a photocell. The output from the photocell is fed through another amplifier to an output terminal from which a signal may be directly coupled to an oscilloscope for visual determination of signal communication.
Huntley U.S. Pat. No. 4,012,633 teaches a system for transmitting low level analog signals which uses a frequency modulator and a photo-diode for converting incoming electrical signals into frequency modulated light signals which are transmitted either by a fiber optic bundle or through air to a photo-transistor to convert the optical signals back to electrical signals.
Ward et al. U.S. Pat. No. 4,119,948 describes a remote meter reading system for electric power meters wherein signals are generated, digitized, and stored representing the amount of power used. In response to interrogation by laser radiation pulses from a remote source, the stored signals can be transmitted to the remote source by emitted pulses of laser radiation.
Deczky U.S. Pat. No. 4,294,682 teaches a data acquisition system for a hot metal handling operation such as an aluminum pot-line wherein a mobile service crane is provided with a transceiver and a second transceiver is mounted in a stationary position on a wall of the building. Information concerning an individual aluminum reduction pot is optically transmitted from the transceiver on the crane to the stationary transceiver via laser or light emitting diode. The stationary transceiver is, in turn, linked to a computer which will issue certain commands for adjustment of the parameters controlling the pot based on this data. These commands are also optically transmitted from the stationary transceiver back to the mobile transceiver.
Harris U.S. Pat. No. 4,408,307 discloses an optical transmission system wherein status and seismic data from remote digital data acquisition units is transmitted via an optical fiber cable to a master station The master station also uses an optical fiber cable to transmit command signals back to the digital acquisition units
Bagby U.S. Pat. No. 4,556,280 teaches the use of a single optical fiber cable for two way transmission of signals between a central station and a remote station, using a shutter element in the remote location movable between two positions. The shutter element and the interior of the housing surrounding the end of the cable have cooperating light reflecting and light absorbing surfaces which are effective in one position of the shutter element to absorb unmodulated light transmitted from the central station over the cable to the remote location and prevent the same from being transmitted back over the cable In the other position of the shutter element, unmodulated light, transmitted to the remote station, is reflected back over the cable to the central station
McGlade U.S. Pat. No. 4,651,571 discloses a strain sensor system wherein a crystal element at a first location is caused to vibrate at its resonant frequency by pulses of light from a laser at a second location, which pulses are transmitted along an optical fiber to the crystal element. A signal derived from this vibration is amplified and then used to control the pulses of a light emitting diode which is also at the first location These pulses from the LED are transmitted along another optical fiber back to the second location.
Despite the fact, however, that many systems have been proposed for the transmission of data via optical fibers from remote locations, including even provision for the use of optical fibers for control of the data transmission, there remains a need for a battery operated remote optical fiber data transmission system wherein the battery may be remotely switched between power and standby states to conserve energy and the entire system may be remotely calibrated, including temperature compensation, with low battery drain. Furthermore, the system should be able to optically transmit the data in a proportional, preferably linear, manner to achieve data integrity, in addition to digital pulse transmission.